1. Field of the Invention
The present invention generally relates to a frame member for a tennis racket, and more particularly to a frame member suitable for use in a tennis racket designed for children or players of slight muscular power which is made of a fiber reinforced resin compact in size and light weight, but having superior strength and vibration absorbing properties.
2. Description of Prior Art
The recent increasing popularity of tennis brings an early start of play even from children, and therefore a compact tennis racket light in weight is strongly desired for such small players, particularly a tennis racket which does not promote tennis elbow and with a high vibration absorbing property is desired. This also applies to a tennis racket for players having slight power.
In general, a frame member for a tennis racket has conventionally been made of a fiber reinforced resin which is composed of, as is known, (1) a continuous fiber/resin matrix or (2) a short or chopped fiber/resin matrix.
For the resin matrix (1), a thermosetting resin such as epoxy, polyester or phenol resin is used. The thermosetting resin is infiltrated into a continuous filament, which is heated and pressurized to thereby set and form the resin into a desired shape.
On the other hand, the resin matrix (2) above consists of a fiber reinforced member of short discontinuous fibers having a reinforcing member dispersed at random in the resin matrix. Either of the two thermoplastic and thermosetting resins can be employed for the resin matrix (2) which is formed mainly through injection molding.
The frame member for a tennis racket should possess strong toughness, rigidity, resilience and vibration absorbing characteristics. Particularly, the racket frame for children's use is necessary to be compact in size and light in weight as well while maintaining the above-mentioned characteristics.
The fiber reinforced resin of the above type (1) contains 60-70 weight % of reinforcing fibers having high rigidity such as carbon fibers, thereby realizing necessary toughness and bending elasticity. However, the epoxy resin or polyester resin used as the matrix resin is inferior in toughness.
Although it has been considered to increase the weight of the reinforcing fibers contained in the resin so as to increase the toughness and rigidity, the vibration absorbability of the racket is undesirably degraded and the weight of the racket as a whole is increased. The amount of reinforcing fibers is naturally increased particularly in the case of the racket frame designed for children since the racket for children should be smaller in size while maintaining strength and rigidity. Therefore, the conventional racket frame for children is eventually heavy in weight with reduced vibration absorbability, whereby the tennis elbow referred to above is easily brought about to the player's elbow at the side with the racket.
Meanwhile, the molecular weight of the matrix resin in the fiber reinforced resin of the above type (2) is small in consideration of the fluidity at the injection molding. At the same time, reinforcing fibers are contained at 30% by weight or so. In many cases, the length of a fiber is not longer than 1 mm after the fibers are turned into pellets and injection-molded. Since the matrix resin having a low molecular weight is used and the reinforcing fibers are very short in length, the strength of the frame member of the type (2) is considerably lowered. Therefore, the racket frame may be broken during the use. Moreover, if it happens that the tennis racket with gut is accommodated in a trunk of a motor vehicle at 80.degree. C. or higher, it may be deformed. Although these inconveniences might be covered by making the racket frame thick, in such a case, the resulting racket frame is heavy in weight and is therefore not suitable particularly for children and players of small power.
As described hereinabove, the conventional frame member for a tennis racket has such disadvantages as poor vibration absorbing property and heavy weight the like. The vibration absorbing property is especially important for the children's racket frame, because it is more undesirable to growing children as compared with adults to have shocks on the elbow. Accordingly, it is necessary to reduce the burden on the elbow as much as possible in order for the children with a future to continue playing for a long time.